WASHINGTON (CNN) -- The bid for the White House between leading Democratic hopefuls Sens. Barack Obama, D-Illinois, and Hillary Clinton, D-New York, is turning ugly, with Clinton criticizing Obama as inexperienced on national security and Obama firing back at what he called a "fabricated controversy."

Sens. Hillary Clinton and Barack Obama are continuing an argument started at Monday's CNN YouTube debate.

The sparring began Monday at the CNN/YouTube debate, in which a viewer asked candidates if they would be willing to meet with leaders of Iran, Syria, Cuba, Venezuela and North Korea -- whom the United States has called rogue leaders.

Obama said he would, adding "it is a disgrace that we have not spoken to them." He added: "The notion that somehow not talking to countries is punishment to them -- which has been the guiding diplomatic principle of this administration -- is ridiculous."

Obama cited the diplomacy of late presidents John F. Kennedy and Ronald Reagan, who engaged the Soviet Union even as he called it the "evil empire."

Obama said one of his first orders of diplomacy in the Middle East would be to "send a signal that we need to talk to Iran and Syria because they're going to have responsibilities if Iraq collapses."

"They have been acting irresponsibly up until this point," he said. "But if we tell them that we are not going to be a permanent occupying force, we are in a position to say that they are going to have to carry some weight, in terms of stabilizing the region."

Clinton, who on the campaign trail has blasted the Bush administration for not engaging Iran and Syria directly, responded to the question by promising "vigorous diplomacy," including using high level envoys.

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But she said she would not meet with such leaders in her first year before knowing what their intentions would be. "We're not going to just have our president meet with Fidel Castro [of Cuba] and Hugo Chavez [of Venezuela] and, you know, the president of North Korea, Iran and Syria until we know better what the way forward would be," Clinton said. "I don't want to be used for propaganda purposes."

Both campaigns issued memorandums the next day highlighting talking points on the exchange and criticizing the other. That was followed by dueling interviews with Iowa's Quad-City Times.

"I thought that was very irresponsible and frankly naive to say you would commit to meeting with Chavez and Castro or others within the first year," Clinton told the paper, adding that Obama regretted his answer at the debate.

Her comments reflected a strategy to paint herself, a two-term senator and former first lady, as the candidate with the most experience to be president and Obama, a junior senator, as too inexperienced to be commander in chief.

Obama struck back at Clinton in his interview with the Quad-City Times, accusing Clinton of a "fabricated controversy."

"I didn't say these guys were going to come for a cup of coffee some afternoon," Obama told the newspaper. Then, referring to Clinton's vote in Congress authorizing the war in Iraq, Obama said: "If there is anything irresponsible and naive it was to authorize George Bush to send 160,000 young American men and women into Iraq apparently without knowing how they were going to get out."

Wendy Sherman, a Clinton supporter who traveled with former Secretary of State Madeline Albright to North Korea to meet with Kim Jong Il, said that engagement was important but the manner in which diplomacy is conducted "matters a great deal."

"One wants to change the manner in which we engage other countries around the world and do so without fear, but do so in a prepared and thoughtful way, so that we get to success and we protect American national security."

Charles Kupchan with the Council on Foreign Relations said that Obama and Clinton were essentially saying the same thing, which is that dialogue is important. "Talking face to face with a head of state, even if that state is a 'rogue' nation, doesn't mean that you give any ground," Kupchan said. "It is simply a way of opening the corridors of communication."

He noted that although the Bush administration took office vowing not to talk to North Korea or Iran, it reached a deal on North Korea's nuclear program through negotiations and now is sitting down with Iran to talk about the violence in Iraq.

"At the end of the day, history suggests that only if we talk to our adversaries do we resolve disputes," Kupchan said.E-mail to a friend